Wastepaper has long served as a source of the raw fiber materials used in papermaking. Traditionally, fiber from wastepaper was utilized only in the production of low grade paper and paperboard products. Today, however, greater utilization of reclaimed fiber (about 25 percent of the total fiber used in papermaking) has provided incentive for taking steps to upgrade the reclaimed product, including treatments to effectively remove ink from the waste fibers.
Because of its quantity, waste newsprint is a particularly important feedstock to such reclamation processes.
It is known in the art that the removal of ink from wastepaper can be accomplished in a process in which the paper is reduced to a pulp and the pulp is contacted with an aqueous medium containing a surfactant "deinking agent". It is further recognized in the prior art that ethoxylates of aliphatic alcohols are useful surfactant deinking agents in such deinking processes. Such alkanol ethoxylates are mixtures of compounds of the formula RO--CH.sub.2 CH.sub.2 O--.sub.n H, where R is an alkyl moiety and n is an integer. Compounds of the mixture have a characteristic distribution of their values for n.
One such prior art process of particular relevance to the present invention is that described by D. C. Wood et al in U.S. Pat. No. 4,162,186. The process described and claimed in that patent involves the use of a deinking agent which necessarily comprises both a water-soluble nonionic surfactant and an oil-soluble nonionic surfactant, in a respective weight ratio of between 6:1 and 3:1. Oil-soluble surfactants are exemplified by ethoxylates of aliphatic C.sub.5 to C.sub.20 alcohols having an average of from about 0.5 to 3.5 oxyethylene units in the molecule, while water-soluble nonionic surfactants are exemplified by ethoxylates of aliphatic C.sub.5 to C.sub.20 alcohols having an average of from about 7 to 50 oxyethylene units in the molecule.
A significant drawback associated with the use in such processes of water-soluble ethoxylated aliphatic alcohol deinking agents is their tendency to enhance foaming in the aqueous deinking medium. Foaming in the papermill system is known (see, for example, R. E. Freis, "Reduced Temperature Deinking", Proceedings of the Technical Association of the Pulp and Paper Industry, 1980 Pulping Conference, pp. 121-125) to cause: (1) reduced efficiency in screens, deckers, cleaners and washers; (2) undesirable variations and flaws in papermaking; and (3) ecological problems in the process effluent.